1. Field of the Invention
The present invention relates to a brushless DC outer rotor motor which is used as a spindle motor for driving a magnetic disk of a thin and small magnetic recording unit.
2. Description of the Prior Art
In a motor 21 which is shown in FIGS. 4 to 7 and rotatably drives a recording medium or disk such as magnetic disks, optical disks and like disks in a recording unit, there is provided a drive pin 10 on its hub base 3 adapted to be loaded with the disk.
The drive pin 10 engages with a reference hole formed in a hub portion of the disk, and is adapted to drive the disk upon energizing of the motor. As shown in FIG. 5, the drive pin 10 is mounted on a free end of a leaf spring 12 which has its base portion fixedly mounted on an lower surface of the hub base 3 by means of screws and like fasteners, thus allowing the leaf spring 12 to urge the drive pin 10 to extend above the upper surface of the hub base 3 or disk-loading surface side through a through-hole 13 formed in the hub base 3.
When the disk is set in a reference position of the hub base 3, the drive pin 10 enters the reference hole of the disk to engage with the disk. However, when the disk is set in any other position of the hub base 3 except the reference position thereof, the drive pin 10 receives the weight of the disk and is depressed thereby so that the leaf spring 12 is resiliently pushed towards the lower side of the hub base 3 against its resiliency, as shown in FIG. 4 by a dotted line.
In operation, since the hub base 3 is rotatably driven when the motor is energized, it is necessary to provide a space for permitting the leaf spring 12 to pass therethrough when the disk is set in any other position except the reference position, the space being provided under the lower side of the hub base 3. Due to the above reason, the hub base 3 is not directly provided in the rotor yoke 2 of the motor, but fixedly mounted on an end portion of a rotary shaft or spindle 4, the end portion being on the opposite side from the rotor yoke 2.
The reason why the hub base 3 is not mounted on the rotor yoke 2 is that although the housing 22 for the bearings 5 for the supporting the spindle 4 of the motor is press-fitted to an inner one 9a of inner and outer double hubs 9a, 9b formed in the central portion of a stator 8, it is not possible to provide an ample space between the front ends of vertical needle terminals 17 and the inner surface of the rotor yoke 2, and therefore the free end of the leaf spring 12 is prevented from easily passing therebetween when the disk is set in any other position except the reference position. Because in the space between the inner and outer double hubs 9a, 9b, there are provided various parts such as the vertical needle terminals 17 connected with wires leading to coils 14 of the stator's pole plates, as shown in FIGS. 6 and 7, such ample space can not be provided therebetween.
When the space between the front ends of the vertical needle terminals 17 and the inner surface of the rotor yoke 2 is increased, it is possible for the thus resiliently bent leaf spring 12 to pass therebetween. However, this poses the problem of requiring the motor to have a large height, which makes it impossible to use a motor with a thin thickness.
Further, in the motor of the recording unit, there are provided an indexing magnet in the rotor yoke 2 of the motor for detecting a reference starting position in recording of the disk and a magnetic detection device (which is constructed of a Hall device for detecting the indexing magnet) on a printed board.
In a conventional motor 21, as shown in FIGS. 14 and 15 the indexing magnet 19 is mounted on an outer peripheral surface of the rotor yoke 2 of the motor 21 and the magnetic detection device 20 is fixedly mounted on the printed board 18 so as to be disposed outside the rotor yoke 2.
As described above, in the conventional motor 21, since the indexing magnet 19 is mounted on the outer peripheral surface of the rotor yoke 2 of the motor 21, it is necessary to precisely determine positions of both the indexing magnet and the drive pin provided in the hub base in assembling. When these positions are not determined properly in assembling, magnetic recording properties of the recording unit becomes unstable, which is a problem inherent in the conventional motor.
In addition, since the indexing magnet extends horizontally outward from the outer periphery of the rotor yoke and the magnetic detection device for detecting it is provided on the printed board in the position outside the rotor yoke, it is actually impossible to provide other components on the printed board near the rotor yoke. Consequently, hitherto the printed board is not effectively used in its component-packaging space, and, therefore it is not possible for the motor to cope with the need that the motor should be smaller in size.